Electric machine rotor

ABSTRACT

An electric machine rotor that is configured to rotate about a first axis includes a plurality of plates and plurality of permanent magnets. The plurality of plates are stacked along the first axis. Each of the plates defines V-shaped pairs of cavities. Each V-shaped pair of cavities defines a pole arc angle. Each cavity has a permanent magnet pocket and a magnetic field guide chamber extending radially outward from the permanent magnet pocket relative to the first axis. Offset angles between the magnetic field guide chambers and the permanent magnet pockets vary within each plate. The plates are stacked such that the permanent magnet pockets between adjacent plates are axially aligned and such that the magnetic field guide chambers between adjacent plates are axially offset. Each permanent magnet extends through a set of permanent magnet pockets.

TECHNICAL FIELD

The present disclosure relates to a rotor for a permanent magnetelectric machine.

BACKGROUND

Electric machines typically employ a rotor and stator to produce torque.Electric current flows through the stator windings to produce a magneticfield. The magnetic field generated by the stator may cooperate withpermanent magnets within the rotor to generate torque.

SUMMARY

An electric machine rotor that is configured to rotate about a firstaxis includes a plurality of plates and plurality of permanent magnets.The plurality of plates are stacked along the first axis. Each of theplates defines V-shaped pairs of cavities. Each V-shaped pair ofcavities defines a pole arc angle. Each cavity has a permanent magnetpocket and a magnetic field guide chamber extending radially outwardfrom the permanent magnet pocket relative to the first axis. Offsetangles between the magnetic field guide chambers and the permanentmagnet pockets vary within each plate. The plates are stacked such thatthe permanent magnet pockets between adjacent plates are axially alignedand such that the magnetic field guide chambers between adjacent platesare axially offset. Each permanent magnet extends through a set ofpermanent magnet pockets. Each permanent magnet pocket within each setof permanent magnet pockets are axially aligned relative to each other.Each set of permanent magnet pockets includes one permanent magnetpocket from each plate.

An electric machine rotor includes a plurality of plates. The pluralityof plates are stacked along a first axis. Each of the plates definesV-shaped pairs of cavities. Each V-shaped pair of cavities defines apole arc angle. Each cavity has a permanent magnet pocket and a magneticfield guide chamber extending radially outward from the permanent magnetpocket relative to the first axis. Offset angles between the magneticfield guide chambers and the permanent magnet pockets vary within atleast one of the V-shaped pairs of cavities and do not vary within atleast one of the V-shaped pairs of cavities within each plate. Theplates are stacked such that the permanent magnet pockets betweenadjacent plates are axially aligned and such that the magnetic fieldguide chambers between adjacent plates are axially offset.

An electric machine rotor includes a plurality of plates. The pluralityof plates stacked along a first axis. Each of the plates definesV-shaped pairs of cavities. Each V-shaped pair of cavities defines apole arc angle. Each cavity has a permanent magnet pocket and a magneticfield guide chamber extending radially outward from the permanent magnetpocket relative to the first axis. Offset angles between the magneticfield guide chambers and the permanent magnet pockets varies between atleast a first and a second of the V-shaped pairs of cavities within eachplate such that each plate defines at least two different pole arcangles. The plates are stacked such that the permanent magnet pocketsbetween adjacent plates are axially aligned and such that the magneticfield guide chambers between adjacent plates are axially offset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a first embodiment of a rotor lamination;

FIG. 1B is a cross-sectional view taken along line 1B-1B of FIG. 1A of arotor section comprised of a stack of laminations from FIG. 1A;

FIG. 2 is a plan view of a section of the rotor lamination comprisingarea A from FIG. 1A;

FIG. 3 is a perspective view of a rotor section comprised of a stack oflaminations from FIG. 1A;

FIG. 4A is a plan view of a second embodiment of a rotor lamination;

FIG. 4B is a cross-sectional view taken along line 4B-4B of FIG. 4A of arotor section comprised of a stack of laminations from FIG. 4A;

FIG. 5 is a plan view of a section of the rotor lamination comprisingarea B from FIG. 4A;

FIG. 6 is a reoriented plan view of a section of the rotor laminationcomprising area C from FIG. 4A;

FIG. 7 is a perspective view of a rotor section comprised of a stack oflaminations from FIG. 4A;

FIG. 8 is a first alternative of the second embodiment of the rotorlamination from FIG. 4A;

FIG. 9 is a second alternative of the second embodiment of the rotorlamination from FIG. 4A;

FIG. 10 is a perspective view of a stator; and

FIG. 11 is a perspective view of an electric machine having a stator anda rotor.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments may take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the embodiments. Asthose of ordinary skill in the art will understand, various featuresillustrated and described with reference to any one of the figures maybe combined with features illustrated in one or more other figures toproduce embodiments that are not explicitly illustrated or described.The combinations of features illustrated provide representativeembodiments for typical applications. Various combinations andmodifications of the features consistent with the teachings of thisdisclosure, however, could be desired for particular applications orimplementations.

Electric machines may be characterized by an undesirable oscillation intorque, which is caused by harmonics present in the airgap flux and inthe airgap permeance. This torque ripple is caused by harmonics that canbe substantially mitigated through proper rotor design. Permanentmagnets may be positioned or oriented about the rotor of the electricmachine in different ways to generate desirable magnetic fields. Each ofthe poles may be formed by a single permanent magnet oriented with onepole (i.e., north or south) in the radially outward direction. The polesof the rotor may be formed by groups of permanent magnets arranged tocooperatively form magnetic poles. One such arrangement orients themagnets in a V-shaped pattern. The interior portion of the “V” hassimilar magnetic poles that cooperate to form a magnetic pole of therotor. An 8-pole rotor includes eight V-shaped patterns disposed aboutthe rotor and spaced by 45°. Each of the permanent magnets may bedisposed in pockets or cavities to retain the permanent magnets. Thesepockets or cavities are typically rectangular and sized to receive thepermanent magnets. The pockets may also include cavities that extend atopposite ends of the pockets and beyond the permanent magnets to limitmagnetic flux leakage between north and south poles of the individualpermanent magnets. The portions of the pockets or cavities that receivethe permanent magnets may be referred to as permanent magnet pockets orcavities. The extended portions of the pockets may be referred to asmagnetic field guide pockets, cavities, or chambers or may be referredto as magnetic field forming pockets, cavities, or chambers. Voids orcavities in the rotor core impede magnetic flux because a vacuum has arelatively low magnetic permeability compared to the rotor core material(e.g., electric steel).

The magnetic field guide chambers associated with each of the pocketsmay adjust the pole arc angle of the magnetic pole. Each of the magneticpoles of an eight pole rotor is designated in a 45° portion of the rotorlamination. This 45° portion is referred to as a mechanical pole pitch.Instead of allowing all of the magnetic poles to have an arc angle of45°, the field forming chambers may be defined to guide the flux fromeach pole by reducing or widening the arc angle. The resulting arc anglefrom each of the poles may still accumulate to cover the entire 360°outer peripheral surface of the rotor or cover less than the entireouter peripheral surface of the rotor.

The rotor may be comprised of a plurality of laminations or laminatedplates that are sequentially stacked in an axial direction along an axisof rotation of the rotor of the electric machine. The laminations areindividually fabricated from a material such iron or steel. Thelaminations are then aligned in an axial direction (i.e., along the axisof rotation of the rotor) to form the rotor or the electric machine. Thelaminations may be stacked “loose”, welded, or bonded together dependingthe desired application. The laminations may include a thin layer ofinsulating material (e.g., a thin layer of epoxy that is approximately0.001 mm thick). There may or may not be small spaces between adjacentlaminations at locations where the adjacent laminations are not affixedto each other, if the application requires the adjacent laminations tobe affixed to each other (i.e., via welding or bonding).

Referring now to FIG. 1A, a first embodiment of a lamination 110 for arotor is shown. The lamination 110 may define a plurality of cavities112 adapted to hold permanent magnets in pockets. The center of thesection 10 may define a circular central opening 114 with a keyway 116for accommodating a driveshaft that may receive a drive key (not shown).The cavities may be oriented such that the permanent magnets (not shown)housed in the cavities 112 form eight alternating magnetic poles 130,132. It is well known in the art that an electric machine may havevarious numbers of poles. The magnetic poles 130 may be configured to benorth poles and the magnetic poles 132 may be configured to be southpoles, or vice versa. The permanent magnets may also be arranged withdifferent patterns. As shown in FIG. 1A, the cavities 112, which holdpermanent magnets, are arranged in pairs that form V-shapes 134.Referring now to FIG. 1B, a plurality of laminations 110 may form asection 10 of the rotor. The rotor has a circular central opening 114for accommodating a driveshaft (not shown).

Referring now to FIG. 2 , the section comprising area A from FIG. 1A isshown having a particular pole arc angle 102. The pole arc angle isshaped by the angle of the magnetic field guide chambers 106 relative tothe magnet pockets 108. The section 10 may have a mechanical pole pitch109 of 45°, as shown.

The pole arc angle 102 can be measured using a variety of methods. Asshown, the pole arc angle 102 is measured as the angle between the mostdistinguished inner corner of the most radially outward portion ofmagnetic field guide chambers 106 from the central axis of the rotor.The pole arc angle 102 can also be measured from the outermost edges ofthe magnetic field guide chambers 106, the inner edges of the magneticfield guide chambers 106, or a hypothetical center of gravity (e.g., ifthe chamber was filled with a material, the center of gravity of thatmaterial). The pole arc angle 102 can also be measured as an angle 104between the permanent magnet pockets 108 and magnetic field guidechambers 106. The angle 104 may be referred to as an orientation angleor an offset angle between the permanent magnet pockets 108 and magneticfield guide chambers 106. The two offset angles 104 between the magnetpockets 108 and magnetic field guide chambers 106 within each pair ofV-shaped pair of cavities 112 differ such that there is an offset angle111 between the center of the mechanical pole pitch 109 and the centerof the pole arc angle 102.

The pole arc angle 102 may also be measured using the length of the arc105 across the outer periphery of the rotor to define a surface. Thesurface may be defined by the length of the arc having a thresholdmagnitude of magnetic flux. For example, the shape of the features,chambers, may make it difficult to ascertain a generic definition andvalue for the pole arc angle. Under these circumstances, the magneticflux crossing the arc length 105 or surface may be measured or estimatedto determine the formed magnetic field. Measuring the result of thefield-forming chamber may provide an improved indication of the desiredpole arc angle instead of measuring the angle directly. This additionalmethod may indirectly provide a comparison between the pole arc anglesof the adjacent sections to determine whether magnetic skewing is usedto reduce torque ripple.

The vertex for the angle may be determined as an intersection of anextension of the V-shaped permanent magnet pockets, an extension of thechambers, or a combination thereof. The vertex of the pole arc angle mayalso be the centroid of the section or lamination or the axis ofrotation of the rotor.

In at least one other embodiment, the pole arc angles are defined by amagnet angle 103 and the orientation angle 104 relative to the magnetangle. The orientation angle 104 has a vertex defined at a point alongan intersection of the pocket 108 and the chamber 106. One leg of theorientation angle is defined by a centerline passing through a centroidof the pocket 108. The centerline may be defined based on a center ofmass or symmetry of the pocket. The other of the legs of the angle maybe defined by a centerline passing through a centroid of the chamber106. The centerline may be defined based on density or symmetry of thechamber. Any of the aforementioned methods or combinations thereof maybe used to determine the pole arc angle.

The orientation or bending angles 104 may be determined by therelationship described in Equation (1):

$\begin{matrix}{\beta = {270^{\bullet} - \alpha - {\tan^{- 1}\frac{{R_{r}{\cos\left( \frac{\theta}{2} \right)}} - R_{c} - {w_{m}\cos\;\alpha}}{{R_{r}{\sin\left( \frac{\theta}{2} \right)}} - {w_{m}\sin\;\alpha}}}}} & (1)\end{matrix}$where β, which is the orientation angle 104, is equal to a function ofthe magnet angle α 103, the width of the permanent magnet pocket w_(m)107, the pole arc angle θ102, the radial distance (i.e., the distancefrom the center of rotor) to the inner vertex 113 of the V-shaped magnetpocket, R_(c), and the rotor outer radius, R_(r).

The orientation angle 104, β, may be set between an angle relative tothe magnet angle 103, α, as disclosed in Equation (2):(180°−α)≤β≤(270°−α)  (2)

Other features (e.g., holes, cavities) generally included on rotorlaminations to control magnetic fields may be included or not includedto properly form magnetic fields in the air gap.

The offset angle 111 may alternatively be defined as the offset betweenthe center of the mechanical pole pitch 109 and the center of the polearc as defined by any of the other variety methods (e.g., the offsetangle 111 may be defined as the offset angle between the center of themechanical pole pitch 109 and the center of angle 102 or angle 105). Thepole arc angles are shown to be the same within each pair of V-shapedpair of cavities 112.

Referring now to FIG. 3 , several laminations 110 are stacked to form aportion of a rotor. The sections have aligned permanent magnet pockets108, which are retaining permanent magnets 115. Each of the permanentmagnets 115 extends through a set of permanent magnet pockets 117. Eachpermanent magnet pocket 108 within each set 117 of permanent magnetpockets 108 may be axially aligned relative to each other (i.e., may bealigned in a direction that is substantially parallel to the axis ofrotation of the rotor). Substantially parallel may refer to anyincremental angle that is between exactly parallel and 15° from exactlyparallel. Each set of permanent magnet pockets 117 includes onepermanent magnet pocket 108 from each lamination 110. Although only fourlaminations 110 are illustrated in FIG. 3 , it should be understood thateach set 117 of permanent magnet pockets 108 may comprise a set ofaxially aligned magnet pockets that includes one magnetic pocket fromeach of the laminations 110 of the rotor if the rotor includes more thanfour laminations and that a single permanent magnet 115 may extendthrough all of the pockets 108 within a set of permanent magnet pockets117 that includes all of the laminations of the rotor.

The field forming chambers 106 form offset pole arc angles relative tothe mechanical pole pitch 109 to create magnetic skewing without skewingthe magnets, which reduces axial flux leakage and increases torqueproduction of the electric machine that includes the rotor. Thelaminations 110 are stacked such that the magnetic field guide chambers106 between one or more the adjacent laminations 110 (or adjacentsections of two or more laminations 110) are axially offset (i.e., areoffset or misaligned in a direction that is substantially parallel tothe axis of rotation of the rotor) in order to further produce magneticskewing without skewing the magnets.

Each of the laminations 110 has a front surface 121 and a rear surface123. In order to reduce manufacturing costs, the V-shaped pairs ofcavities 112 of each lamination may form an identical pattern thatextends axially with respect to the axis of rotation of the rotor 125from the front surface 121 to the rear surface 123. A first of thelaminations 110 may be flipped or rotated about a second axis 127 thatis perpendicular to the axis of rotation of the rotor 125 such that therear surface 123 of the first of the laminations 110 contacts the rearsurface 123 of a second of the laminations 110 within the stack. A thirdof the laminations 110 may be flipped or rotated about a third axis 129that is perpendicular to the axis of rotation of the rotor 125 such thatthe front surface 121 of the third of the laminations 110 contacts thefront surface 121 of a fourth of the laminations 110 within the stack.The second axis 127 and the third axis 129 may be radially offset (asshown) to each other relative to the axis of rotation of the rotor 125or may be radially aligned to each other relative to the axis ofrotation of the rotor 125. However, it should be noted that in order tomaintain alignment of the keyways 116 of each lamination 110 within thestack, the second axis 127 and third 129 axis will need to be radiallyaligned to each other relative to the axis of rotation of the rotor 125and will need to extend through the centers of the keyways 116. Thesecond axis 127 and third axis 129 may be defined as the center line ofa mechanical pole pitch (e.g., the second axis 127 as shown) or along anouter edge of any one of the mechanical pole pitches 109, which is alsoat the boundary between any of the adjacent mechanical pole pitches 109(e.g., third axis 129), in order maintain axial alignment within eachset of permanent magnet pockets 117.

The flipping or rotating of laminations 110 relative to each other aboutan axis that is perpendicular to the axis of rotation of the rotor 125produces the axial offsetting of the magnetic field guide chambers 106between adjacent laminations 110 when one of the adjacent laminations110 has been flipped or rotated. Alternatively, if the pole arc anglesare also different between one or more of the pair of V-shaped pair ofcavities 112, the axial offsetting of the magnetic field guide chambers106 may be accomplished by rotating adjacent laminations relative toeach other about the axis of rotation of the rotor 125 by one or moremechanical pole pitches 109.

FIG. 3 , depicts an ABBA rotor configuration, where the middle twolaminations have been flipped relative to the outer two laminations. Asshown, the permanent magnets are aligned such that minimal magneticfield leakage occurs between the sections. This configuration would alsoallow a single permanent magnet to traverse through each of sections,instead of multiple permanent magnets. An alternative BAAB rotor can beobtained by swapping the stacking sequence of section A and B (notshown). Other alternatives may also be ABAB or BABA. The rotor mayinclude several stacks of one of the configurations (e.g., the rotor mayinclude four stacks of the ABBA configuration) or may include severalstacks of different configurations in any combination (e.g., the rotormay include four stacks, one with an ABBA configuration, one with a BAABconfiguration, one with an ABAB configuration, and one with and BAABconfiguration).

Although the embodiment described in FIGS. 1A-3 depicts laminations 110where the offset angles 104 between the permanent magnet pockets 108 andmagnetic field guide chambers 106 differ within each pair of V-shapedcavities, this disclosure should be construed to include laminationswhere the offset angles between the permanent magnet pockets andmagnetic field guide chambers differ within one or more pairs ofV-shaped cavities. Furthermore, although the embodiment described inFIGS. 1A-3 depicts the same pole arc angles within each pair of V-shapedpair of cavities 112, this disclosure should be construed to includelaminations where the pole arc angles and the offset angles 104 maydiffer between two or more of the pairs of V-shaped cavities.

Referring now to FIG. 4A, a second embodiment of a lamination 210 for arotor is shown. The lamination 210 may define a plurality of cavities212 adapted to hold permanent magnets in pockets. The center of thesection 20 may define a circular central opening 214 with a keyway 216for accommodating a driveshaft that may receive a drive key (not shown).The cavities may be oriented such that the permanent magnets (not shown)housed in the cavities 212 form eight alternating magnetic poles 230,232. It is well known in the art that an electric machine may havevarious numbers of poles. The magnetic poles 230 may be configured to benorth poles and the magnetic poles 232 may be configured to be southpoles, or vice versa. The permanent magnets may also be arranged withdifferent patterns. As shown in FIG. 4A, the cavities 212, which holdpermanent magnets, are arranged in pairs that form V-shapes 234.Referring now to FIG. 4B, a plurality of laminations 210 may form asection 20 of the rotor. The rotor has a circular central opening 214for accommodating a driveshaft (not shown).

Referring now to FIG. 5 , the section comprising area B from FIG. 4A isshown having a particular pole arc angle 202. The pole arc angle isshaped by the angle of the magnetic field guide chambers 206 relative tothe magnet pockets 208. The section 20 may have a mechanical pole pitch209 of 45°, as shown.

The pole arc angle 202 can be measured using a variety of methods. Asshown, the pole arc angle 202 is measured as the angle between the mostdistinguished inner corner of the most radially outward portion ofmagnetic field guide chambers 206 from the central axis of the rotor.The pole arc angle 202 can also be measured from the outermost edges ofthe magnetic field guide chambers 206, the inner edges of the magneticfield guide chambers 206, or a hypothetical center of gravity (e.g., ifthe chamber was filled with a material, the center of gravity of thatmaterial). The pole arc angle 202 can also be measured as an angle 204between the permanent magnet pockets 208 and magnetic field guidechambers 206. The angle 204 may be referred to as an orientation angleor an offset angle between the permanent magnet pockets 208 and magneticfield guide chambers 206. The two offset angles 204 between the magnetpockets 208 and magnetic field guide chambers 206 in the pair ofV-shaped pair of cavities 212 are the same but may differ from theoffset angles 204 in other pairs V-shaped pair of cavities on thelamination 210 (see offset angles 304 below).

The pole arc angle 202 may also be measured using the length of the arc205 across the outer periphery of the rotor to define a surface. Thesurface may be defined by the length of the arc having a thresholdmagnitude of magnetic flux. For example, the shape of the features,chambers, may make it difficult to ascertain a generic definition andvalue for the pole arc angle. Under these circumstances, the magneticflux crossing the arc length 205 or surface may be measured or estimatedto determine the formed magnetic field. Measuring the result of thefield-forming chamber may provide an improved indication of the desiredpole arc angle instead of measuring the angle directly. This additionalmethod may indirectly provide a comparison between the pole arc anglesof the adjacent sections to determine whether magnetic skewing is usedto reduce torque ripple.

The vertex for the angle may be determined as an intersection of anextension of the V-shaped permanent magnet pockets, an extension of thechambers, or a combination thereof. The vertex of the pole arc angle mayalso be the centroid of the section or lamination or the axis ofrotation of the rotor.

In at least one other embodiment, the pole arc angles are defined by amagnet angle 203 and the orientation angle 204 relative to the magnetangle. The orientation angle 204 has a vertex defined at a point alongan intersection of the pocket 208 and the chamber 206. One leg of theorientation angle is defined by a centerline passing through a centroidof the pocket 208. The centerline may be defined based on a center ofmass or symmetry of the pocket. The other of the legs of the angle maybe defined by a centerline passing through a centroid of the chamber206. The centerline may be defined based on density or symmetry of thechamber. Any of the aforementioned methods or combinations thereof maybe used to determine the pole arc angle.

The orientation or bending angles 204 may be determined by therelationship described in Equation (1) where β, which is the orientationangle 204, is equal to a function of the magnet angle α 203, the widthof the permanent magnet pocket w_(m) 207, the pole arc angle θ 202, theradial distance (i.e., the distance from the center of rotor) to theinner vertex 213 of the V-shaped magnet pocket, R_(c), and the rotorouter radius, R_(r).

The orientation angle 204, β, may be set between an angle relative tothe magnet angle 203, α, as disclosed in Equation (2) above. Otherfeatures (e.g., holes, cavities) generally included on rotor laminationsto control magnetic fields may be included or not included to properlyform magnetic fields in the air gap.

Referring now to FIG. 6 , the section comprising area C from FIG. 4A isshown having a particular pole arc angle 302. The pole arc angle isshaped by the angle of the magnetic field guide chambers 306 relative tothe magnet pockets 308. The section 20 may have a mechanical pole pitch309 of 45°, as shown. The section comprising area C has been reorientedin FIG. 6 relative to FIG. 4A for illustrative purposes.

The pole arc angle 302 can be measured using a variety of methods. Asshown, the pole arc angle 302 is measured as the angle between the mostdistinguished inner corner of the most radially outward portion ofmagnetic field guide chambers 306 from the central axis of the rotor.The pole arc angle 302 can also be measured from the outermost edges ofthe magnetic field guide chambers 306, the inner edges of the magneticfield guide chambers 306, or a hypothetical center of gravity (e.g., ifthe chamber was filled with a material, the center of gravity of thatmaterial). The pole arc angle 302 can also be measured as an angle 304between the permanent magnet pockets 308 and magnetic field guidechambers 306. The angle 304 may be referred to as an orientation angleor an offset angle between the permanent magnet pockets 308 and magneticfield guide chambers 306. The two offset angles 304 between the magnetpockets 308 and magnetic field guide chambers 306 in the pair ofV-shaped pair of cavities 312 are the same but may differ from theoffset angles 304 in other pairs V-shaped pair of cavities on thelamination 210 (see offset angles 204 above).

The pole arc angle 302 may also be measured using the length of the arc305 across the outer periphery of the rotor to define a surface. Thesurface may be defined by the length of the arc having a thresholdmagnitude of magnetic flux. For example, the shape of the features,chambers, may make it difficult to ascertain a generic definition andvalue for the pole arc angle. Under these circumstances, the magneticflux crossing the arc length 305 or surface may be measured or estimatedto determine the formed magnetic field. Measuring the result of thefield-forming chamber may provide an improved indication of the desiredpole arc angle instead of measuring the angle directly. This additionalmethod may indirectly provide a comparison between the pole arc anglesof the adjacent sections to determine whether magnetic skewing is usedto reduce torque ripple.

The vertex for the angle may be determined as an intersection of anextension of the V-shaped permanent magnet pockets, an extension of thechambers, or a combination thereof. The vertex of the pole arc angle mayalso be the centroid of the section or lamination or the axis ofrotation of the rotor.

In at least one other embodiment, the pole arc angles are defined by amagnet angle 303 and the orientation angle 304 relative to the magnetangle. The orientation angle 304 has a vertex defined at a point alongan intersection of the pocket 308 and the chamber 306. One leg of theorientation angle is defined by a centerline passing through a centroidof the pocket 308. The centerline may be defined based on a center ofmass or symmetry of the pocket. The other of the legs of the angle maybe defined by a centerline passing through a centroid of the chamber306. The centerline may be defined based on density or symmetry of thechamber. Any of the aforementioned methods or combinations thereof maybe used to determine the pole arc angle.

The orientation or bending angles 304 may be determined by therelationship described in Equation (1) where β, which is the orientationangle 304, is equal to a function of the magnet angle α 303, the widthof the permanent magnet pocket w_(m) 307, the pole arc angle θ302, theradial distance (i.e., the distance from the center of rotor) to theinner vertex 313 of the V-shaped magnet pocket, R_(c), and the rotorouter radius, R_(r).

The orientation angle 304, β, may be set between an angle relative tothe magnet angle 303, α, as disclosed in Equation (2) above. Otherfeatures (e.g., holes, cavities) generally included on rotor laminationsto control magnetic fields may be included or not included to properlyform magnetic fields in the air gap.

Referring now to FIG. 7 , several laminations 210 are stacked to form aportion of a rotor. The sections have aligned permanent magnet pockets208, 308 which are retaining permanent magnets 215. Each of thepermanent magnets 215 extend through a set of permanent magnet pockets217. Each permanent magnet pocket 208, 308 within each set 217 ofpermanent magnet pockets 208, 308 may be axially aligned relative toeach other (i.e., may be aligned in a direction that is substantiallyparallel to the axis of rotation of the rotor). Substantially parallelmay refer to any incremental angle that is between exactly parallel and15° from exactly parallel. Each set of permanent magnet pockets 217includes one permanent magnet pocket 208, 308 from each lamination 210.Although only four laminations 210 are illustrated in FIG. 7 , it shouldbe understood that each set 217 of permanent magnet pockets 208, 308 maycomprise a set of axially aligned magnet pockets that includes onemagnetic pocket from each of the laminations 210 of the rotor if therotor includes more than four laminations and that a single permanentmagnet 215 may extend through all of the pockets 208, 308 within a setof permanent magnet pockets 217 that includes all of the laminations ofthe rotor.

The field forming chambers 206, 306 form different pole arc angles tocreate magnetic skewing without skewing the magnets, which reduces axialflux leakage and increases torque production of the electric machinethat includes the rotor. The laminations 210 are stacked such that themagnetic field guide chambers 206, 306 between one or more the adjacentlaminations 210 (or adjacent sections of two or more laminations 210)are axially offset (i.e., are offset or misaligned in a direction thatis substantially parallel to the axis of rotation of the rotor) in orderfurther produce the magnetic skewing without skewing the magnets.

Each of the laminations 210 has a front surface 221 and a rear surface223. In order to reduce manufacturing costs, the V-shaped pairs ofcavities 212 of each lamination may form an identical pattern thatextends axially with respect to the axis of rotation of the rotor 225from the front surface 221 to the rear surface 223. A first of thelaminations 210 may be flipped or rotated about a second axis 227 thatis perpendicular to the axis of rotation of the rotor 225 such that therear surface 223 of the first of the laminations 210 contacts the rearsurface 223 of a second of the laminations 210 within the stack. A thirdof the laminations 210 may be flipped or rotated about a third axis 229that is perpendicular to the axis of rotation of the rotor 225 such thatthe front surface 221 of the third of the laminations 210 contacts thefront surface 221 of a fourth of the laminations 210 within the stack.The second axis 227 and the third axis 229 may be radially offset (asshown) to each other relative to the axis of rotation of the rotor 225or may be radially aligned to each other relative to the axis ofrotation of the rotor 225. However, it should be noted that in order tomaintain alignment of the keyways 216 of each lamination 210 within thestack, the second axis 227 and third axis 229 will need to be radiallyaligned to each other relative to the axis of rotation of the rotor 225and will need to extend through the centers of the keyways 216. Thesecond axis 227 and third axis 229 may be defined as the center line ofa mechanical pole pitch (e.g., the second axis 227 as shown) or along anouter edge of any one of the mechanical pole pitches 209, which is alsoat the boundary between any of the adjacent mechanical pole pitches 209(e.g., third axis 229), in order maintain axial alignment within eachset of permanent magnet pockets 217.

The flipping or rotating of laminations 210 relative to each other aboutan axis that is perpendicular to the axis of rotation of the rotor 225produces the axial offsetting of the magnetic field guide chambers 206,306 between adjacent laminations 210 when one of the adjacentlaminations 210 has been flipped or rotated. Alternatively, the axialoffsetting of the magnetic field guide chambers 206, 306 may beaccomplished by rotating adjacent laminations relative to each otherabout the axis of rotation of the rotor 225 by one or more mechanicalpole pitches 209.

FIG. 7 , depicts an ABBA rotor configuration, where the middle twolaminations have been flipped relative to the outer two laminations. Asshown, the permanent magnets are aligned such that minimal magneticfield leakage occurs between the sections. This configuration would alsoallow a single permanent magnet to traverse through each of sections,instead of multiple permanent magnets. An alternative BAAB rotor can beobtained by swapping the stacking sequence of section A and B (notshown). Other alternatives may also be ABAB or BABA. The rotor mayinclude several stacks of one of the configurations (e.g., the rotor mayinclude four stacks of the ABBA configuration) or may include severalstacks of different configurations in any combination (e.g., the rotormay include four stacks, one with an ABBA configuration, one with a BAABconfiguration, one with an ABAB configuration, and one with and BAABconfiguration).

The embodiment described in FIGS. 4A-7 depicts laminations 210 where theoffset angles 204, 304 between the permanent magnet pockets 208, 308 andmagnetic field guide chambers 206, 306 are the same within each pair ofV-shaped cavities but differ between adjacent pairs of V-shapedcavities, resulting in a difference between the length of the pole arcangle 202 and the length of pole arc angle 302 (i.e., the length of thepole arc angle 202≠the length of pole arc angle 302). The embodimentdescribed in FIGS. 4A-7 also depicts laminations 210 where the offsetangles 204, 304 between the permanent magnet pockets 208, 308 andmagnetic field guide chambers 206, 306 are identical in every of pair ofV-shaped cavities. This disclosure, however, should be construed toinclude laminations where the offset angles between the permanent magnetpockets and magnetic field guide chambers are the same within each pairof V-shaped cavities but differ between two or more of the pairs ofV-shaped cavities, or where the offset angles between the permanentmagnet pockets and magnetic field guide chambers differ within at leastone of the pairs of V-shaped cavities and differ between two or more ofthe pairs of V-shaped cavities.

Referring now to FIG. 8 , a first alternative embodiment of thelamination 310 where the offset angle between the permanent magnetpockets and magnetic field guide chambers differs between two or morepairs the V-shaped cavities is illustrated. Specifically, the embodimentin FIG. 8 depicts eight pairs of V-shaped cavities where the offsetangle between the permanent magnet pockets and magnetic field guidechambers differs between every V-shaped pair of cavities in a series offour pairs of V-shaped cavities, but is the same in every fourth pair ofV-shaped cavities resulting in different pole arc angles between everyV-shaped pair of cavities in the series of four pairs of V-shapedcavities but the same pole arc angles repeating every fourth pair ofV-shaped cavities. Such a configuration has a total of four differentpole arc angles θ_(a), θ_(b), θ_(c), and θ_(d). Please note thatθ_(a)≠θ_(b)≠θ_(c)≠θ_(d). In order to reduce manufacturing costs, theV-shaped pairs of cavities of each lamination 310 may form an identicalpattern that extends axially with respect to the axis of rotation of arotor formed by the laminations 310.

In a stack of laminations 310, each having the configuration illustratedin FIG. 8 , every first lamination may not be rotated, every secondlamination may be rotated about a first axis 312, every third laminationmay be rotated about a second axis 314, and every fourth lamination maybe rotated about a third axis 316 such that the orientations of within astack of the laminations repeats in a pattern of four in order toproduce the axial offsetting of the magnetic field guide chambersbetween adjacent laminations 310 (e.g., see FIGS. 3 and 7 ) in orderproduce the magnetic skewing without skewing the magnets.

Rotating the laminations 310 to the produce the axial offsetting of themagnetic field guide chambers between adjacent laminations 310, includesrotating the laminations approximately 180° about the respective axes.The first axis 312, second axis 314, and third axis 316 may all beperpendicular to an axis of rotation of a rotor formed by laminations310 having the configuration illustrated in FIG. 8 but may all be offsetradially to each other relative to the axis of rotation. The first axis312, second axis 314, and third axis 316 may be defined as the centerline of a mechanical pole pitch (e.g., the second axis 314) or along anouter edge of any one of the mechanical pole pitches, which is also atthe boundary between any of the adjacent mechanical pole pitches (e.g.,first axis 312), in order to produce the axial offsetting of themagnetic field guide chambers between adjacent laminations 310 whilemaintaining axial alignment within each set of permanent magnet pockets.Alternatively, the axial offsetting of the magnetic field guide chambersbetween adjacent laminations 310 may be accomplished by rotatingadjacent laminations relative to each other about the axis of rotationof the rotor by one or more mechanical pole pitches. For example, everyfirst lamination may not be rotated, every second lamination could berotated one mechanical pole pitch, every third lamination could berotated two mechanical pole pitches, and every fourth lamination couldbe rotated three mechanical pole pitches.

Referring now to FIG. 9 , a second alternative embodiment of thelamination 410 where the offset angle between the permanent magnetpockets and magnetic field guide chambers differs between two or morepairs the V-shaped cavities is illustrated. Specifically, the embodimentin FIG. 9 depicts eight pairs of V-shaped cavities where the offsetangle between the permanent magnet pockets and magnetic field guidechambers differs between every V-shaped pair of cavities resulting indifferent pole arc angles between every V-shaped pair of cavities. Sucha configuration has a total of eight different pole arc angles θ_(a),θ_(b), θ_(c), θ_(d), θ_(e), θ_(f), θ_(g), and θ_(h). Please note thatθ_(a)≠θ_(b)≠θ_(c)≠θ_(d)≠θ_(e)≠θ_(f)≠θ_(g)≠θ_(h). In order to reducemanufacturing costs, the V-shaped pairs of cavities of each lamination410 may form an identical pattern that extends axially with respect tothe axis of rotation of a rotor formed by the laminations 410.

In a stack of laminations 410, each having the configuration illustratedin FIG. 9 , every first lamination may not be rotated, every secondlamination may be rotated about a first axis 412, every third laminationmay be rotated about a second axis 414, every fourth lamination may berotated about a third axis 416, every fifth lamination may be rotatedabout a fourth axis 418, every sixth lamination may be rotated about afifth axis 420, every seventh lamination may be rotated about a sixthaxis 422, every eighth lamination may be rotated about a seventh axis424 such that the orientations of within a stack of the laminationsrepeats in a pattern of eight in order to produce the axial offsettingof the magnetic field guide chambers between adjacent laminations 410(e.g., see FIGS. 3 and 7 ) in order produce the magnetic skewing withoutskewing the magnets.

Rotating the laminations 410 to the produce the axial offsetting of themagnetic field guide chambers between adjacent laminations 410, includesrotating the laminations approximately 180° about the respective axes.The first axis 412, second axis 414, and third axis 416, fourth axis418, fifth axis 420, sixth axis 422, and seventh axis 424 may all beperpendicular to an axis of rotation of a rotor formed by laminations410 having the configuration illustrated in FIG. 9 but may all be offsetradially to each other relative to the axis of rotation. The first axis412, second axis 414, and third axis 416, fourth axis 418, fifth axis420, sixth axis 422, and seventh axis 424 may be defined as the centerline of a mechanical pole pitch (e.g., the second axis 414) or along anouter edge of any one of the mechanical pole pitches, which is also atthe boundary between any of the adjacent mechanical pole pitches (e.g.,first axis 412), in order to produce the axial offsetting of themagnetic field guide chambers between adjacent laminations 410 whilemaintaining axial alignment within each set of permanent magnet pockets.Alternatively, the axial offsetting of the magnetic field guide chambersbetween adjacent laminations 410 may be accomplished by rotatingadjacent laminations relative to each other about the axis of rotationof the rotor by one or more mechanical pole pitches. For example, everyfirst lamination may not be rotated, every second lamination could berotated one mechanical pole pitch, every third lamination could berotated two mechanical pole pitches, every fourth lamination could berotated three mechanical pole pitches, every fifth lamination could berotated four mechanical pole pitches, every sixth lamination could berotated five mechanical pole pitches, every seventh lamination could berotated six mechanical pole pitches, and every eighth lamination couldbe rotated seven mechanical pole pitches.

Now referring to FIGS. 10 and 11 , a stator 40 is shown. The stator 40has teeth 43 and stator winding cavities or slots 45 to support a set ofstator windings. The stator 40 may surround a rotor 14 having aplurality of rotor sections from any of the embodiments described hereinhaving permanent magnet pockets arranged therein. Some of the sectionsare not shown. The difference between the pole arc angle may be equal tothe slot pitch 42 of the stator. The slot pitch 42 is the mechanicalangle between adjacent slots arranged around the entire stator 40. Forexample, a 48-slot stator 40 has a slot pitch 42 of 7.5 degrees. Thedifference between the pole arc angles may be equal to the slot pitch 42of the stator 40.

The words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments may becombined to form further embodiments that may not be explicitlydescribed or illustrated. While various embodiments could have beendescribed as providing advantages or being preferred over otherembodiments or prior art implementations with respect to one or moredesired characteristics, those of ordinary skill in the art recognizethat one or more features or characteristics may be compromised toachieve desired overall system attributes, which depend on the specificapplication and implementation. As such, embodiments described as lessdesirable than other embodiments or prior art implementations withrespect to one or more characteristics are not outside the scope of thedisclosure and may be desirable for particular applications.

What is claimed is:
 1. An electric machine rotor configured to rotateabout a first axis comprising: a plurality of plates stacked along thefirst axis, each of the plates defining V-shaped pairs of cavities, eachV-shaped pair of cavities defining a pole arc angle, each cavity havinga permanent magnet pocket and a magnetic field guide chamber extendingradially outward from the permanent magnet pocket relative to the firstaxis, wherein offset angles between the magnetic field guide chambersand the permanent magnet pockets varies within each plate, wherein theplates are stacked such that the permanent magnet pockets betweenadjacent plates are axially aligned and such that the magnetic fieldguide chambers between adjacent plates are axially offset, wherein eachof the plates of the plurality of plates has a front surface and a rearsurface, wherein the V-shaped pairs of cavities of each plate form anidentical pattern that extends axially with respect to the first axisfrom the front surface to the rear surface, and wherein a first of theplurality of plates is rotated about a second axis that is perpendicularto the first axis such that the rear surface of the first plate contactsthe rear surface of a second plate within the stack; and a plurality ofpermanent magnets, each permanent magnet extending through a set ofpermanent magnet pockets, wherein each permanent magnet pocket withineach set of permanent magnet pockets are axially aligned relative toeach other, and wherein each set of permanent magnet pockets includesone permanent magnet pocket from each plate.
 2. The electric machinerotor of claim 1, wherein the offset angles between the magnetic fieldguide chambers and the permanent magnet pockets varies within at leastone of the V-shaped pairs within each plate.
 3. The electric machinerotor of claim 1, wherein the offset angles between the magnetic fieldguide chambers and the permanent magnet pockets varies between at leasta first of the V-shaped pairs and a second of the V-shaped pairs withineach plate.
 4. The electric machine rotor of claim 1, wherein a third ofthe plurality of plates is rotated about a third axis that isperpendicular to the first axis such that the front surface of the thirdplate contacts the front surface of a fourth plate within the stack. 5.The electric machine rotor of claim 4, wherein the second axis and thethird axis are radially offset to each other relative to the first axis.6. The electric machine rotor of claim 4, wherein a first of theplurality of plates is rotated about the first axis such that the firstplate contacts and is offset one or more mechanical pole pitches from anadjacent plate.
 7. The electric machine rotor of claim 1, wherein atleast a first and a second of the V-shaped pairs of cavities within eachplate define at least two non-equal pole arc angles.
 8. The electricmachine rotor of claim 1, wherein at least a first, a second, a third,and a fourth of the V-shaped pairs of cavities within each plate defineat least four non-equal pole arc angles.
 9. An electric machine rotorcomprising: a plurality of plates stacked along a first axis, each ofthe plates defining V-shaped pairs of cavities, each V-shaped pair ofcavities defining a pole arc angle, each cavity having a permanentmagnet pocket and a magnetic field guide chamber extending radiallyoutward from the permanent magnet pocket relative to the first axis,wherein offset angles between the magnetic field guide chambers and thepermanent magnet pockets vary within at least one of the V-shaped pairsof cavities and do not vary within at least one of the V-shaped pairs ofcavities within each plate, wherein the plates are stacked such that thepermanent magnet pockets between adjacent plates are axially aligned andsuch that the magnetic field guide chambers between adjacent plates areaxially offset, wherein each of the plates of the plurality of plateshas a front surface and a rear surface, wherein the V-shaped pairs ofcavities of each plate form an identical pattern that extends axiallywith respect to the first axis from the front surface to the rearsurface, and wherein a first of the plurality of plates is rotated abouta second axis that is perpendicular to the first axis such that the rearsurface of the first plate contacts the rear surface of a second platewithin the stack.
 10. The electric machine rotor of claim 9, wherein athird of the plurality of plates is rotated about a third axis that isperpendicular to the first axis such that the front surface of the thirdplate contacts the front surface of a fourth plate within the stack. 11.The electric machine rotor of claim 10, wherein the second axis and thethird axis are radially offset to each other relative to the first axis.12. The electric machine rotor of claim 9, wherein at least a first anda second of the V-shaped pairs of cavities within each plate define atleast two non-equal pole arc angles.
 13. The electric machine rotor ofclaim 9, wherein at least a first, a second, a third, and a fourth ofthe V-shaped pairs of cavities within each plate define at least fournon-equal pole arc angles.
 14. An electric machine rotor comprising: aplurality of plates stacked along a first axis, each of the platesdefining V-shaped pairs of cavities, each V-shaped pair of cavitiesdefining a pole arc angle, each cavity having a permanent magnet pocketand a magnetic field guide chamber extending radially outward from thepermanent magnet pocket relative to the first axis, wherein offsetangles between the magnetic field guide chambers and the permanentmagnet pockets varies between at least a first and a second of theV-shaped pairs of cavities within each plate such that each platedefines at least two different pole arc angles, wherein the plates arestacked such that the permanent magnet pockets between adjacent platesare axially aligned and such that the magnetic field guide chambersbetween adjacent plates are axially offset, and wherein a first of theplurality of plates is rotated about the first axis such that the firstplate contacts and is offset one or more mechanical pole pitches from anadjacent plate.
 15. The electric machine rotor of claim 14, wherein eachof the plates of the plurality of plates has a front surface and a rearsurface, and wherein the V-shaped pairs of cavities of each plate forman identical pattern that extends axially with respect to the first axisfrom the front surface to the rear surface.
 16. The electric machinerotor of claim 15, wherein a first of the plurality of plates is rotatedabout a second axis that is perpendicular to the first axis such thatthe rear surface of the first plate contacts the rear surface of asecond plate within the stack.
 17. The electric machine rotor of claim16, wherein a third of the plurality of plates is rotated about a thirdaxis that is perpendicular to the first axis such that the front surfaceof the third plate contacts the front surface of a fourth plate withinthe stack.
 18. The electric machine rotor of claim 17, wherein thesecond axis and the third axis are radially offset to each otherrelative to the first axis.
 19. The electric machine rotor of claim 14,wherein at least the first, the second, a third, and a fourth of theV-shaped pairs of cavities within each plate define at least fournon-equal pole arc angles.
 20. The electric machine rotor of claim 14,wherein at least the first, the second, a third, a fourth, a fifth, asixth, a seventh, and an eighth of the V-shaped pairs of cavities withineach plate define at least eight non-equal pole arc angles.